Control mechanism



Aprilv 2, 1946.

MMIII-' Il,"

W. M.'HURsT CONTROL MECHANISM K Filed Aug. 1, 1944 BVI/t4 A RNEY Kaff.

Patented Apr. 2, 1946 CONTROL MECHANISM William M.`Hurst, Douglaston, N. Y., assignor to Hazeltne Corporation, Washington, D. C., a corporation of Delaware Application August 1, 1944, Serial No. 547,636

14 Claims.

This invention is directed to a control mechanism. While being subject to a variety of applications, the invention is especially` suited for controlling the variable element of an adjustably tuned circuit and will be described in that connection.

As is well known, adjustably tuned circuits are utilized very generally in communication, electronic, and similar apparatus. Where the apparatus is operated in the ultra-high portion of the frequency spectrum, the adjustably tuned circuit frequently consists of a variable inductor, tuned by a condenser which may be comprised in Whole or in part of the inherent capacitance of the inductor and related stray capacitances. In suche case, the operating frequency of the tuned circuit is usually controlled through the adjustment of a tuning core or slug associated with the inductor and effective to determine the apparent inductance thereof in accordance with the degree of coupling therebetween. One form of control mechanism. employed to vary the position Of the tuning slug and thereby vary the inductance and operating frequency of vthe tuned circuit, includes a threaded shaft to one end of which the tuning slug is secured. A control knob afxed to the opposite end of the shaft facilitates accurate tuning adjustments. While such prior art control mechanisms permit the tuned circuit to be adjusted over a given range of operating frequencies, they generally do not include provisions for arresting the control mechanism at preselected control positions, as is required to adjust the tuned circuit rapidly and accurately to one or more desired Operating frequencies Within its range. In some installations, such a feature is highly desirable.

Other control mechanisms enabling a tuned circuit to be adjusted over a given operating frequency range and including provisions for rapidly adjusting the circuit to one or more predetermined frequencies within the range have already been proposed. They are commonly referred to in the art as push-button tuning devices and are usually associated with an adjustably tuned circuit in which the variable element is an air-dielectric condenser, including a stator and a co-Operating rotor. Such arrangements comprise more or less complicated mechanical structures for controlling the position of the rotor of the variable condenser. In addition to their mechanical complexities, these arrangements represent a substantial mass or Weight which may be objectionable in applications where the weight factor is important, as in airborne installations.

It is an object of the present invention, therefore, to provide a control mechanism which is not subject to one or more of the above-,mentioned limitations of prior art arrangements.

It is another object of the invention to provide an improved control mechanism having a simpliiied and inexpensive mechanical construction.

lt is another object of the invention to provide an improved control mechanism which permits continuous adjustment of a controlled element and includes provisions for quickly and accurately effecting preselected adjustments of the controlled element.

A control mechanism, inv accordance with the invention, comprises a rotatable shaft to be coupled to a controlled element for exertingthereon a control effect determined by the rotational displacement of the shaft with respect to a reference position and means for angularly displacing the shaft with respect to its reference position. The control mechanism includes a rst stop member, a threaded member vhaving an arcuate conguration, and means for supporting such members for` relative rotation therebetween in response to rotation of the rotatable shaft. At least one cooperating stop member is adjustably supported by the threaded member in a preselected position to register with the iirst stop member and arrest the shaft in a corresponding preselected controlled position. A locking device is provided for the co-operating stop member, having a resilient portion disposed in such relation to the threaded member as yieldably to engage the co-operating stop member in any position of adjustment thereof to permit adjustment of the co-operating stop member to its preselected position by rotation on the threaded member, while locking the cooperating stop member against movement due to relative movement between the first stop member and the threaded member.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is an elevational View, partly in cross section, of a control mechanism in accordance with the invention; Fig. 2 is a crosssectional view taken as indicated by directional arrows 2--2 of Fig. 1; Fig. 3 is an end elevation taken as indicated by directional arrows 3-3 of Fig. l; While Fig. 4 represents a portionof the Fig. 1 arrangement in modified form.

Referring now more particularly to Fig. 1 of the `proved conductivity characteristic.

- through the use of a nonmagnetic material.

drawing,V there is illustrated a control mechanism embodying the invention utilized for controlling an adjustably tuned circuit. YThe tuned circuit may constitute a component of a wave-signal translating apparatus, such as a Wave-signal receiver, but since the invention may be completely understood from a consideration of the adjustment of the tuned circuit alone, the remainder of the apparatus has been omitted from the drawing.

The tuned circuit is provided by a parallel combination of a variable inductor L and a condenser C, represented in broken-line construction since it may be comprised in Whole or in part of the inherent capacitance of the inductor and stray capacitances associated therewith.l Inductor L is supported by a cylindrical coil form I of a suitable insulating material, as, for example, a thermoplastic resin. A coil-retaining groove II in the form of a continuous spiral is milled into coil 'form I0 and the wall thickness of the coil form vis, preferably, as small as practical.

preferably, made of a resilient material such as hard drawn brass, silverY plated to have an irn- The cross section of the coil conductor and the material from which it is formed are selected with referenceto the coil diameter so that the free ends I2 and I3v thereof have sufficient self-rigidity to permit direct connection to other circuit components of the equipment. In assembling therdescribed inductor arrangement, thepreformed coil is threaded on to coil form I with the convolutions thereof received bygroovel II. Due to the vresiliency of the coil and the relative dimensions of the coil diameter and groove diameter, the coil convolutions rmly engage groove II and se- VThe described tuned circuit is adjustable over a curely lock the Ycoil in a desired position on form Y Agiven range of operating frequencies through a 'tuning core or slug I4 which is freely movable Tuning slug I4 may be of tuning slug'is effective to vary the apparent inductance of inductor L in accordance with the coupling therebetween. Where the slug is of magnetic material, the inductance increases With this cbupling while the converse effect is obtained able shaft to be mechanically coupled to the controlled element, plunger I 5, for exerting thereon a control effect determined by the rotational displacement of the shaft With respect to a reference position, identified hereinafter. Shaft 25 is rotatable Within and supported by an externally threaded bushing 26. One end of bushing 26 projects through aligned apertures in 'strap 24 Aof bracket 23 and mounting plate 2D, this end of the bushing being 'spun over as indicated at 21 to complete an assembly of the mounting plate, bracket and bushing.

c A control knob 3l constitutes means for angularly displacing sh'aft .25 with respect to a reference position. This control knob is locked by Way of a set screw 32 to an elongated hub' 33, the latter being affixed to one end of shaft 25 through a transverse pin 34 which projects through both th'e hub and shaft. A cam means the arrangement under consideration, tuning slug I4 is preferably a nonmagnetic silver sleeve. The slug diameterY is only slightly less'than the inner diameter of coi1 form I0 so that maximum coupling with'inductor L and maximum tuning efciency result. Slug I4 is suitably secured to one -ticul'arlyg stop member 5`is a resilient wipingv end of a plunger-I 5, constituting the element controlledlby the control mechanism presently to be by a U-shaped Vbracket v23 and is aiiixed throughv a transverse strap 24 thereof to mounting platev 20. Bracket 23 is partially brokenvavvay in Fig. 1 to revealth'e driving connectionrto plunger I 5.

Considering now the control mechanism of Fig.

l, the illustrated arrangement comprisesarotat- 35 secured to the opposite end of shaft 25 is effective mechanically to couple the shaft to plunger I5. The cam is a length of resilient material, such as a section of brass rod, formed to the general configuration of an Archimedean spiral. One end 35 of the formed cam is inserted into an axially disposed socket provided in shaft 25 while the opposite end 31 abuts against the periphery of the shaft. Both such' ends of the cam are retained in their described relation with shaft 25 through soldering or Welding.r In order that the cam may engage plunger i5, a segment of coil form I adjacent the cam-is cut away, as illus-V trated in Fig. l, and the cam is proportioned so as toproject therethrough.. A coil spring 38 anchored to a vertical projection 39 of bracket 23 is connected with the free end of plunger I5, thereby constituting means for biasing the controlled element intoV engagement with cam 35. A Washer 28 carried by shaft 25 holds the shaft `against axial displacement within bushing 26 resulting from the bias of spring 38,

A vertical projection -40 which vis struck out of strap 24 of bracket 23 engages certain peripheral 'portions of the cam to limit the maximum angular -diate the dened limiting positions is approximately 330 degrees fortheillustrated arrangelrnent.

The control mechanism alsoY includes a first stoprnember 5i) having arecessed detent portion 5I, Fig.'2; a'threaded memb'er52 having an arcuate conguration; and means for supporting these members for relative rotation therebetween in responseto rotation of shaft 25. More parmember mechanically connected with shaft 25 to jbe angularly driven thereby. This mechanical kconnection i'safforded by the free end of hub 33 which projects through and is spun over an aper- "ture in stop member 55,' thereby coaxially supporting this member with referenceV to shaft 25.

Threaded memberl 52 is preferably circular and is provided with a mounting bracket 53. Threaded member 5,2 is vlocked against rotation by being -iixedly supportcdin substantially coaxial alignvment with shaft 25. This is accomplished by a mounting collar63 having Van annular shoulder portion which receives mounting bracket 53. mounting c sollar is coaxially arranged With reference to threaded bushing 26 and a lock nut 64. threaded upon bushing 26, clamps bracket 53 to lock threaded member 52 against rotation.

At least one co-operating stop member is adjustably supported by threaded member 52 in a preselected positionto register with detent portion of stop member 5|) and arrest shaft 25 in a corresponding preselected control position. In its simplest form the co-operating stop device comprises a hexagonal nut 54 threaded on member 52 before the latter is assembled upon its mounting bracket 53. Preferably, a plurality of such co-operating stop members is provided, being individually adjustably supported by member 52 and individually effective in :zo-operation With stop member 5B to arrestthe shaft in one of a corresponding plurality of preselected control positions.

Finally, the control mechanism includes a locking device 55 having a resilient Portion disposed in Such relation to threaded member 52 as yieldably to engage each cooperating stop member 54 in any position of adjustment thereof, to permit adjustment of the fio-operating stop members to their individual preselected positions by rotation 0n member 52 While locking such stop members against any movement resulting from relative rotation between rst stop member 5t and threaded member 52, This locking device is a resilient spider mounted coaxially with and effectivelygsecured to threaded member 52 through collar E3 and lock nut 64. The peripheral portion of the spider has substantially the same configuration as threaded member 52 and is proportioned yieldably to engage each stop member 54.

In considering the operation of the described control mechanism, the function of stop members 50 and 54 will initially be neglected and it will be assumed that control knob 3| is adjusted so that cam portion Ma engages stop projection 49. As indicated above, this condition represents the reference position of shaft in which cam 35 and spring 38 cause tuning slug I4 to beV withdrawn from inductor L so as to have substantially zero coupling therewith. For this condition, the inductor exhibits its natural value of -inductance and tuned circuit L, C has its minimum operating frequency. As control knob 3| is rotated in a clockwise direction, shaft 25 is angularly displaced in the same sense with respect to its reference position. Such displacement of shaft 25 results in the application of a control effect upon plunger l5 through the agency of cam 35. The magnitude of the control effect is determined by the rotational displacement of the shaft and the configuration of the cam. The controlled element l5 and tuning slug |4 carried thereby are laterally displaced a corresponding amount in the direction of inductor L so as to increase the degree of coupling between the inductor and the tuning slug. The increased coupling results in a decrease in apparent inductance of inductor L and a proportional increase in the operating frequency of tuned circuit L, C. In the limiting condition when shaft 25 has its maximum angular displacement, the degree of coupling between the inductor and its tuning slug is a maximum and the operating frequency of the tuned circuit likewise has its maximum value. Thus, the control mechanism is effective continuously to adjust the operating frequency of the tuned circuit L, C over a given range of operating frequencies. Sto-p members 50 and 54 permit the operating frequency to be established accurately and rapidly to predetermined desired-frequencies within this y range in the following manner.

A particular setting of a given stop member 54 represents a predetermined angular displacement with respect to the reference position of shaft 25. Likewise, a given angular displacement of the shaft represents a given controlV effect which causes tuning slug |4 to have a predetermined degree of coupling with inductor L resulting in a given operating frequency of the tuned circuit. Therefore, one or more of Vstop .members 54 'is manually rotated and adjusted to a preselected position or positions along threaded member 52. This adjustment may be readily accomplished in view of the yielding engagement of lock device .55 with these stop members. Having thus selectively positioned stop members 54, control knob 3| is rotated until the detent portion 5| of stop member 5B registers with a particular stop member 54 and arrests shaft '25 in a corresponding preselected control position to establish a desired operating frequency of the tuned circuit. Since stop member 50 is resilient, any of the co-operating stop members 54 may be passed over to eiect registration with a particular one. Thus the shaft 25 may be arrested in a preselected control position corresponding to the adjustment of a particular co-operating stop member 54 irrespective vof the previous setting of control knob 3|.

The operator may easily determine the engagement of detent portion 5| of stop member .50 with a co-operating stop member through the changing resistance to turning which results from the wiping action of stop members 5U and 54. Also, locking device 55 locks co-operating stop members 54 in their desired preselected positions against any movement which might otherwise re-` sult from this wiping action.

The fragmentary View of Fig. 4 illustrates a modified form of the coupling between the rotatable shaft and the controlled element. 'I'his arrangement is generally similar to that of Fig. 1, corresponding components thereof being identined by like reference numerals primed. In the Fig. 4 arrangement, the mounting portion 69 of coil form l0 is offset to have an increased diameter so as to enclose the cam arrangement, presently to be described, which couples shaft 25' with controlled element I5. This cam arrangement comprises a cylinder 10 having a closed end 1| which is xed to the free end of shaft 25 for rotation therewith. A cam track 12 is milled into the cam cylinder. This cam cylinder is in coaxial alignment with shaft 25 and controlled element I5', receiving the latter in its open end.

The plunger of this embodiment carries a. cam

following pin 13 which projects through cam track 12. Pin 13 also engages an internal keyway 14 milled in mounting portion 69 of coil form I0'. A coil spring 15 interposed betweeny the closed end of cam cylinder 10 and the adjacent end of plunger l5' retains pin 13 in engagement with the cam track. Threaded bush-r operating 'stop members. .Such a modification of preselected control For example, the control mechanism may read- Y ily be utilized to control a variable condenser or other controlled element.

The control mechanism of the invention will be I seen to comprise a relatively-few light mechaniv cal elements. Accordingly, it substantially avoids the mechanical complexity of the prior art arrangements mentioned above. Additionally, Athe control mechanism is quiteinexpensive to construct and represents a small mass, rendering it suitable even for airborne installations.

While there have been described 'what are at present considered to be the preferred embodiments of this invention, it will be obvious yto those skilled in the art that various changes and modications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within theY true spirit and scope of the invention.

` VWhat is claimedis: Y Y

'1.`A control mechanism comprising, a rotatable shaft to be coupled to la controlled element for exertingthereon a control effect determined -by the rotational displacement of said shaft with respect to a reference position, means for angularly displacingV said shaft with respect to said referenceposition, a first stop .memben'a threaded member having an arcuate configuration, means Vfor supporting said members for relative rotation therebetween in response to'rotation of Ysaid shaft,

preselected control position, and a locking de-v vice for said co-operating stop member having a resilient portionrdisposed in such relation to said threaded member as yieldably to engage said cooperating stop member in any position of adjustment thereof to Ypermit adjustment of said` co-operating stop member to said preselected ,position by rotation on said threaded member while lockingA said co-operating stop member against movement due to relative rotation between said rst stop member andV said threaded member.

2. A control mechanismv comprising, a rotatable shaft to be coupled to'a controlled element for exerting thereon a control effect, determined by the rotational displacement of said shaft with 1 respect to a reference position, means for angularly displacing said shaft with respect to said reference position, a first stop member, a threaded memberV having'fan "arcuate configuration,

means for 4mechanically connecting one of said ,members to said shaft for rotationV therewith and for locking the other o-f said members against ro- .by said threaded member in a preselected position to register with said rst stop member and arrest said shaft in a corresponding preselected control position, and a locking device for said cooperating stop member having a resilient portion disposed in such relation to said threaded member as yieldably to engage said' co-operating stop member in any position of adjustment thereof to permit adjustment of said co-operatingrstop member to said preselected position by rotation on said threaded member while locking said co` operating stop member against movement due to relative rotation between said first stop member and said threaded member.

3. A control mechanism comprising, a rotatable shaft to be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with lrespect/to said reference position, a first stop member, a threaded member having an arcuate configuration, means for mechanically coupling said first stop member to said shaft tobe angularly driven thereby and for locking said threaded member against rotation to provide relative rotation therebetween in response to rotation of said shaft, at least one co-operating stop member adjustably supported by said threaded member in aV preselected position to register with said rst stop member and arrest said shaft in a corresponding preselected control position, and a locking device for said co-operating stop member-having a resilient portion disposed in such relation to Vsaid threaded member as yieldably to engage said cof operating stop member in'any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member while locking said co-operating stop member against movement due to relative rotation between said rst stop member and said threaded member.

4. A control mechanism comprising, a rotatable shaft to be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for-angularly displacing said shaft with respect to said reference position, a first stop member, a' threaded member having an yarcuate configuration, means for mechanically supporting saidfrst stop member on said shaft for rotation therewith and' for fixedly supporting said 4threaded member in substantially coaxial alignment with said shaft to provide relative rotation between said members `in response to rotation of said shaft, at least one cooperating stop member adjustably supported by said threaded member in a preselected member as yieldably to engage said co-operating stopmember in any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member while locking said cooperating stop member against movement due to relative rotation between said first stop member and said threaded member. Y

' 5. A control mechanism comprising, a rotatable shaft to be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position, a first stop member, a substantially circular threaded member, means for supporting said members for relative rotation therebetween in response to rotation of said shaft, at least one co-operating stop member adjustably supported by said threaded member in a preselected position to register with said rst stop member and arrest said shaft in a corresponding preselected control position, and a locking device for said co-operating stop member having a resilient portion disposed in such relation to said threaded member Aas yieldably to engage said co-operating stop member in any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member while locking said co--operating stop member against movement due to relative rotation between said rst stop member and said threaded member.

6. A control mechanism comprising, a rotatable shaft to be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with respect to said reference position, a first stop member, a threaded member having an arcuate configuration, means for supporting said members for relative rotation therebetween in response to rotation of said shaft, a plurality of co-operating stop members individually adjustably supported by said threaded member in a preselected position and individually effective to register with said first stop member to arrest said shaft in one of a corresponding plurality of preselected control positions, and a locking device for said co-operating stop members having a resilient portion disposed in such relation to said threaded member as yieldably to engage each of said co-operating stop members in any position of adjustment thereof to permit adjustment of said co-operating stop members to said preselected positions by rotation on said threaded member while locking said cooperating stop members against movement due to relative rotation between said first stop member and said threaded member.

7. A control mechanism comprising, rotatable shaft to be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position7 means for angularly displacing said shaft with respect t0 said reference position, a first stop member including a detent portion, a threaded member having an arcuate conguration, means for supporting said members for relative rotation therebetween in response to rotation of said shaft, at least one cooperating stop member adjustably supported by said threaded member in a preselected position t-o register with said detent portion of said first stop member and arrest said shaft in a corresponding preselected control position, and a locking device for said co-operating stop member having a resilient portion disposed in such relation to said threaded member as yieldably to engage said co-operating stop member in any position of adjustment thereof to npermit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member while locking said Cso-operating stop member against movement due to relative rotation between said rst stop member and said threaded member.

8. A control mechanism comprising, a rotatable shaft to be coupled Yto a controlled element for exerting thereon a control effect: determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with respect to said reference position, a first stop member, a threaded member having an arcuate configuration, means for supporting said members for relative rotation therebetween in response to rotation of said shaft, at least one co-operating stop member adiustably supported by said threaded member in a preselected position Vto register with said first stop member and arrest said shaft in a corresponding preselected control position, and a locking device for said co-operating stop member including a resilient portion. having substantially the same configuration as and disposed in such relation to said threaded member as yieldably to engage said (zo-operating stop member in any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member while locking said co-operating stop member against movement due to relative rotation between said first stop member and said threaded member.

9. A control mechanismcomprising, a rotatablei shaft kto be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with respect to said reference position, a rst stop member, a threaded member having an arcuate configuration, means for supporting said members for relative rotation therebetween in response to rotation oi said shaft, at least one co-operating stop member adjustably supported by said threaded member in a preselected position to register with said first stop member and arrest said shaft in a co1'- responding preselected control position, and a circular locking device for said cti-operating stop member arranged in substantially coaxial alignment with said threaded member and having a resilient portion for yieldably engaging said cooperating stop member in any position of adjustment thereof to permit adjustment of said cooperating stop member to said preselected position by rotation on said threaded member while locking said co-operating stop member against movement due to relative ,rotation between said first stop member and said threaded member.

10. A control mechanism comprising, a rotatable shaft to be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with respect to said reference position, a first stopmember, a threaded member having an arcuate configuration, means for supporting said members for relative rotation therebetween in response to rotation of said shaft, at least one cooperating stop member adjustably supported by said threaded member in a preselected position to register with said first stop member and arrest said shaft in a corresponding preselected control position, and a locking device for said co-operating stop member secured to said threaded member and having a resilient portion disposed in such relation to said threaded member as yieldably to engage said co-operating stop member in any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member while locking said cooperating stop member against movement due to relative rotation between'said first stop member and said threadedV member. i

11.`A control mechanism comprising, a rota able shaft to be coupled to a controlled element for exerting thereon a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with Vrespect to said reference position, means for limiting the maximum angular displacement ofsaid shaft to a predetermined value, a first stop member, a threaded member having an arcuate configuration, means for supporting said members for relative rotation therebetween in response to rotation of said shaft, at least one co-operating stop member adjustably supported by said threaded member in a preselected position to register with said first CFI asomo? 1,3. A control mechanism comprising, a rotatable' shaft for exerting on a controlled element a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with respect to said reference position, cam

Y means secured to said shaft and effective to stop member and arrest said shaft in a corresponding preselected control lposition, and a locking device for said co-ope'r-ating, stop member having a resilient portion disposed in such relation to said threaded member as yieldably to engage said (3o-operating stop member in any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member While locking said co-operating stop member against movement due to relative, rotation between saidV first stop member and said threaded member. Y

12. A control mechanism comprising, a rotatable shaft for exerting on a controlled element a,

control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacing said shaft with respect to said reference position, cam means secured to said shaft and effective to couple said shaft to said controlled element,` a

control position, Vand a locking device for saidv co-operating stop member having a'resilient portion disposed in such relation to said threaded member as yieldably to engage said co-operating stop member in any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member While locking said co-V operating stop member against movement due to 'relative rotation between said first stop member and said threaded member. Y

couple said shaft to said controlled element, means for biasing said controlled element into engagement with said cam means, afirst stop member, a threaded Vmember having an arcuate configuration, means for supporting said-members for relative rotation therebetween in response to rotation of said shaft, at least one co-operating stop member adjustably supported by said threaded member in a preselected position to register with said rst stopmember and arrest said shaft in a corresponding preselected control position, and a locking device for said co-operating stop member having a resilient-portion disposed in such relation to said threaded memberas yieldably to engage said co-operating stop member in anyY position of adjustment thereof to' permit adjustment of said co-operating stop member to.

said preselected position by rotation 'on said threaded'member While locking said co-operating stop member against movement due to rela- V tive rotation between said first stop member land first stop member, a threaded member having an l said threaded member.

14. A control mechanism comprising, a rotatable shait for exerting on a controlled element a control effect determined by the rotational displacement of said shaft with respect to a reference position, means for angularly displacingV said shaft lwith respect to said reference position, cam means arranged in coaxial Valignment with and coupling said shaft and said controlled element. a first stop member, a threaded member having an' arcuate configuration, means for supporting said members for relative rotation therebetween in response to rotation ofsaid shaft, at least one co-operating stop member` adjustably supported by said threaded member in a preselected position to register with said first stop member and arrest said shaft in a corresponding preselected control position, and a locking device for said co-operating stop member having a resilient portion disposed in such relation to said threaded member as yieldably to engage said co-operating stop member in any position of adjustment thereof to permit adjustment of said co-operating stop member to said preselected position by rotation on said threaded member while locking said co-operating stop member against movement dueto relative rotation between said first stop member and said threaded member.

- WILLIAM M. HURST. 

